A number of patents and publications are cited herein in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Each of these references is incorporated herein by reference in its entirety into the present disclosure, to the same extent as if each individual reference was specifically and individually indicated to be incorporated by reference.
Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise,” and variations such as “comprises” and “comprising,” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a pharmaceutical carrier” includes mixtures of two or more such carriers, and the like.
Ranges are often expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment.
This disclosure includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
RAF, Proliferative Disorders, and Cancer
Mutations in genes that directly or indirectly control cell growth and differentiation are generally considered to be the main cause of cancer. Malignant tumors develop through a series of stepwise, progressive changes that lead to the loss of growth control characteristic of cancer cells, i.e., continuous unregulated proliferation, the ability to invade surrounding tissues, and the ability to metastasize to different organ sites. Carefully controlled in vitro studies have helped define the factors that characterize the growth of normal and neoplastic cells and have led to the identification of specific proteins that control cell growth and differentiation.
RAF is key downstream target for the ras GTPase and mediates the activation of the MAP kinase cascade consisting of raf-MEK-ERK. Activated ERK is a kinase that subsequently targets a number of proteins responsible for mediating, amongst other things, the growth, survival and transcriptional functions of the pathway. These include the transcription factors ELK1, C-JUN, the Ets family (including Ets 1, 2, and 7), and the FOS family. The ras-raf-MEK-ERK signal transduction pathway is activated in response to many cell stimuli including growth factors such as EGF, PDGF, KGF etc. Because the pathway is a major target for growth factor action, the activity of raf-MEK-ERK has been found to be upregulated in many factor dependent tumours. The observation that about 20% of all tumours have undergone an activating mutation in one of the ras proteins indicates that the pathway is more broadly important in tumorigenesis. There is growing evidence that activating mutations in other components of the pathway also occur in human tumours. This is true for RAF.
The RAF oncogene family includes three highly conserved genes termed A-RAF, B-RAF and C-RAF (also called Raf-1). RAF genes encode protein kinases that are thought to play important regulatory roles in signal transduction processes that regulate cell proliferation. RAF genes code for highly conserved serine-threonine-specific protein kinases, which are recruited to the plasma membrane following direct binding to the Ras small Guanine-nucleotide binding proteins and this is the initiating event in RAF activation. RAF proteins are part of a signal transduction pathway believed to consist of receptor tyrosine kinases, p21 Ras, RAF protein kinases, Mek1 (ERK activator or MAPKK) kinases and ERK (MAPK) kinases, which ultimately phosphorylate several cellular substrates, including transcription factors. Signaling through this pathway can mediate differentiation, proliferation or oncogenic transformation in different cellular contexts. Thus, RAF kinases are believed to play a fundamental role in the normal cellular signal transduction pathway, coupling a multitude of growth factors to their net effect, cellular proliferation. Because RAF proteins are direct downstream effectors of ras protein function, therapies directed against RAF kinases are believed to be useful in treatment of ras-dependent tumors.
The RAF kinases are differentially regulated and expressed; C-RAF is the most thoroughly characterized and is expressed in all organs and in all cell lines that have been examined. A-RAF and B-RAF also appear to be ubiquitous, but are most highly expressed in urogenital and brain tissues, respectively. Because B-RAF is highly expressed in neural tissues it was once thought to be limited to these tissues but it has since been found to be more widely expressed. Although all RAF proteins can bind to active Ras, B-raf is most strongly activated by oncogenic Ras, and may be the primary target of oncogenic Ras in transformed cells.
Recent evidence indicates that mutational activation of B-RAF is found in a number of different tumours including more than 65% of malignant melanomas, more than 10% of colorectal cancers (Davies, H., et al., 2002, Nature, Vol. 417, pp. 949-954; Rajagopalan, H. et al., 2002, Nature, Vol. 418, p. 934), ovarian cancers (Singer, G., et al., 2003, J. Natl. Cancer Inst., Vol. 95, pp. 484-486) and papillary thyroid cancers (Brose, M., et al., 2002, Cancer Res., Vol. 62, pp. 6997-7000; Cohen, Y., et al., 2003, Invest. Ophthalmol. Vis. Sci., Vol. 44, pp. 2876-2878). A range of different B-RAF mutations have been identified in different tumours with the most common being a V600E mutation in the so-called activation loop of the kinase domain (Davies, H., et al., 2002, Nature, Vol. 417, pp. 949-954).
Other mutations of B-RAF found associated with human cancers may not necessarily activate B-RAF directly but do upregulate the activity of the ras-raf-MEK-ERK pathway by mechanisms which are not fully understood but may involve cross-talk with other RAF isoforms, such as A-RAF (Wan, P., et al., 2004, Cell, Vol. 116, pp. 855-867). In such cases, inhibition of RAF activity would remain a beneficial aim in cancer treatment.
In addition to link between B-RAF and certain cancers, there is a significant amount of evidence to indicate a more broad inhibition of RAF activity could be beneficial as an antitumour therapy. Blocking the pathway at the level of B-RAF would be effective at counteracting the upregulation of this pathway caused by tumourigenic ras mutations and also in tumours responding to growth factor action via this pathway. Genetic evidence in Drosophila and C. elegans indicates that RAF homologues are essential for ras dependent actions on differentiation (Dickson, B., et al., 1993, Nature, Vol. 360, pp. 600-603). Introduction of constitutively active MEK into NIH3T3 cells can have a transforming action whilst expression of dominant negative MEK proteins can suppress the tumourigenicity of ras transformed cell lines (Mansour, S. J., et al., 1994, Science, Vol. 265, pp. 966-970; Cowely, S., et al., 1994, Cell, Vol. 77, pp. 841-852). Expression of a dominant negative raf protein has also been found to inhibit ras dependent signalling as has suppression of raf expression using an antisense oligonucleotide construct (Koch, W., et al., 1991, Nature, Vol. 349, pp. 426-428; Bruder, T. T., et al., 1992, Genes and Development, Vol. 6, pp. 545-556).
This and other evidence suggests that inhibition of RAF (e.g., B-RAF) activity would be beneficial in the treatment of cancer, and that inhibition of RAF (e.g., B-RAF) activity could be particularly beneficial in those cancers containing a constitutively activated B-raf mutation.
The raf-MEK-ERK pathway functions downstream of many receptors and stimuli indicating a broad role in regulation of cell function. For this reason inhibitors of RAF may find utility in other disease conditions that are associated with upregulation of signalling via this pathway. The raf-MEK-ERK pathway is also an important component of the normal response of non-transformed cells to growth factor action. Therefore inhibitors of RAF may be of use in diseases where there is inappropriate or excessive proliferation of normal tissues. These include, but are not limited to glomerulonephritis and psoriasis. The cellular signalling pathway of which RAF is a part has also been implicated in inflammatory disorders characterized by T-cell proliferation (T-cell activation and growth), such as tissue graft rejection, endotoxin shock, and glomerular nephritis.
RAF (e.g., B-RAF) has been shown to be a valid therapeutic target in hyperproliferative disorders such as cancer. Activated versions of RAF (e.g., B-RAF) are able to transform mammalian cells, allowing them to take on the characteristics of cancer cells and the growth of these cells becomes dependent on the mutant RAF (e.g., B-RAF) protein. Inhibition of RAF (e.g., B-RAF) activity in human cancer cell lines that express the mutant forms of RAF (e.g., B-RAF) blocks their growth and ultimately induces their death.
Angiogenesis
Chronic proliferative diseases are often accompanied by profound angiogenesis, which can contribute to or maintain an inflammatory and/or proliferative state, or which leads to tissue destruction through the invasive proliferation of blood vessels. (Folkman, 1997, EXS, Vol. 79, pp. 1-81; Folkman, 1995, Nature Medicine, Vol. 1, pp. 27-31; Folkman and Shing, 1992, J. Biol. Chem., Vol. 267, p. 10931.)
Angiogenesis is generally used to describe the development of new or replacement blood vessels, or neovascularisation. It is a necessary and physiological normal process by which the vasculature is established in the embryo. Angiogenesis does not occur, in general, in most normal adult tissues, exceptions being sites of ovulation, menses and wound healing. Many diseases, however, are characterized by persistent and unregulated angiogenesis. For instance, in arthritis, new capillary blood vessels invade the joint and destroy cartilage (Colville-Nash and Scott, 1992, Ann. Rhum. Dis., Vol. 51, p. 919). In diabetes (and in many different eye diseases), new vessels invade the macula or retina or other ocular structures, and may cause blindness (Brooks et al., 1994, Cell, Vol. 79, p. 1157). The process of atherosclerosis has been linked to angiogenesis (Kahlon et al., 1992, Can. J. Cardiol., Vol. 8, p. 60). Tumor growth and metastasis have been found to be angiogenesis-dependent (Folkman, 1992, Cancer Biol., Vol. 3, p. 65; Denekamp, 1993, Br. J. Rad., Vol. 66, p. 181; Fidler and Ellis, 1994, Cell, Vol. 79, p. 185).
The recognition of the involvement of angiogenesis in major diseases has been accompanied by research to identify and develop inhibitors of angiogenesis. These inhibitors are generally classified in response to discrete targets in the angiogenesis cascade, such as activation of endothelial cells by an angiogenic signal; synthesis and release of degradative enzymes; endothelial cell migration; proliferation of endothelial cells; and formation of capillary tubules. Therefore, angiogenesis occurs in many stages and attempts are underway to discover and develop compounds that work to block angiogenesis at these various stages.
There are publications that teach that inhibitors of angiogenesis, working by diverse mechanisms, are beneficial in diseases such as cancer and metastasis (O'Reilly et al., 1994, Cell, Vol. 79, p. 315; Ingber et al., 1990, Nature, Vol. 348, p. 555), ocular diseases (Friedlander et al., 1995, Science, Vol. 270, p. 1500), arthritis (Peacock et al., 1992, J. Exp. Med., Vol. 175, p. 1135; Peacock et al., 1995, Cell. Immun., Vol. 160, p. 178) and hemangioma (Taraboletti et al., 1995, J. Natl. Cancer Inst., Vol. 87, p. 293).
RTKs
Receptor tyrosine kinases (RTKs) are important in the transmission of biochemical signals across the plasma membrane of cells. These transmembrane molecules characteristically consist of an extracellular ligand-binding domain connected through a segment in the plasma membrane to an intracellular tyrosine kinase domain. Binding of ligand to the receptor results in stimulation of the receptor-associated tyrosine kinase activity that leads to phosphorylation of tyrosine residues on both the receptor and other intracellular proteins, leading to a variety of cellular responses. To date, at least nineteen distinct RTK subfamilies, defined by amino acid sequence homology, have been identified.
FGFR
The fibroblast growth factor (FGF) family of signaling polypeptides regulates a diverse array of physiologic functions including mitogenesis, wound healing, cell differentiation and angiogenesis, and development. Both normal and malignant cell growth as well as proliferation are affected by changes in local concentration of these extracellular signaling molecules, which act as autocrine as well as paracrine factors. Autocrine FGF signaling may be particularly important in the progression of steroid hormone-dependent cancers and to a hormone independent state (Powers et al., 2000, Endocr. Relat. Cancer, Vol. 7, pp. 165-197).
FGFs and their receptors are expressed at increased levels in several tissues and cell lines and overexpression is believed to contribute to the malignant phenotype. Furthermore, a number of oncogenes are homologues of genes encoding growth factor receptors, and there is a potential for aberrant activation of FGF-dependent signaling in human pancreatic cancer (Ozawa et al., 2001, Teratog. Carcinog. Mutagen., Vol. 21, pp. 27-44).
The two prototypic members are acidic fibroblast growth factor (aFGF or FGF1) and basic fibroblast growth factors (bFGF or FGF2), and to date, at least twenty distinct FGF family members have been identified. The cellular response to FGFs is transmitted via four types of high affinity transmembrane tyrosine-kinase fibroblast growth factor receptors numbered 1 to 4 (FGFR-1 to FGFR-4). Upon ligand binding, the receptors dimerize and auto- or trans-phosphorylate specific cytoplasmic tyrosine residues to transmit an intracellular signal that ultimately reaches nuclear transcription factor effectors.
Disruption of the FGFR-1 pathway should affect tumor cell proliferation since this kinase is activated in many tumor types in addition to proliferating endothelial cells. The over-expression and activation of FGFR-1 in tumor-associated vasculature has suggested a role for these molecules in tumor angiogenesis.
FGFR-2 has high affinity for the acidic and/or basic fibroblast growth factors, as well as the keratinocyte growth factor ligands. FGFR-2 also propagates the potent osteogenic effects of FGFs during osteoblast growth and differentiation. Mutations in FGFR-2, leading to complex functional alterations, were shown to induce abnormal ossification of cranial sutures(craniosynostosis), implying a major role of FGFR signaling in intramembranous bone formation. For example, in Apert (AP) syndrome, characterized by premature cranial suture ossification, most cases are associated with point mutations engendering gain-of-function in FGFR-2 (Lemonnier et al., 2001, J. Bone Miner. Res., Vol. 16, pp. 832-845).
Several severe abnormalities in human skeletal development, including Apert, Crouzon, Jackson-Weiss, Beare-Stevenson cutis gyrata, and Pfeiffer syndromes are associated with the occurrence of mutations in FGFR-2. Most, if not all, cases of Pfeiffer Syndrome (PS) are also caused by de novo mutation of the FGFR-2 gene (Meyers et al., 1996, Am. J. Hum. Genet., Vol. 58, pp. 491-498; Plomp et al., 1998, Am. J. Med. Genet., Vol. 75, 245-251), and it was recently shown that mutations in FGFR-2 break one of the cardinal rules governing ligand specificity. Namely, two mutant splice forms of fibroblast growth factor receptor, FGFR2c and FGFR2b, have acquired the ability to bind to and be activated by atypical FGF ligands. This loss of ligand specificity leads to aberrant signaling and suggests that the severe phenotypes of these disease syndromes result from ectopic ligand-dependent activation of FGFR-2 (Yu et al., 2000, Proc. Natl. Acad. Sci. U.S.A., Vol. 97, pp. 14536-14541).
Activating mutations of the FGFR-3 receptor tyrosine kinase such as chromosomal translocations or point mutations produce deregulated, constitutively active, FGFR-3 receptors which have been involved in multiple myeloma and in bladder and cervix carcinomas (Powers, C. J., et al., 2000, Endocr. Rel. Cancer, Vol. 7, p. 165). Accordingly, FGFR-3 inhibition would be useful in the treatment of multiple myeloma, bladder and cervix carcinomas.
VEGFR
Vascular endothelial growth factor (VEGF), a polypeptide, is mitogenic for endothelial cells in vitro and stimulates angiogenic responses in vivo. VEGF has also been linked to inappropriate angiogenesis (Pinedo, H. M., et al., 2000, The Oncologist, Vol. 5 (90001), pp. 1-2). VEGFR(s) are protein tyrosine kinases (PTKs). PTKs catalyze the phosphorylation of specific tyrosyl residues in proteins involved in the regulation of cell growth and differentiation. (Wilks, A. F., 1990, Progress in Growth Factor Research, Vol. 2, pp. 97-111; Courtneidge, S. A., 1993, Dev. Supp.l, pp. 57-64; Cooper, J. A., 1994, Semin. Cell Biol., Vol. 5(6), pp. 377-387; Paulson, R. F., 1995, Semin. Immunol., Vol. 7(4), pp. 267-277; Chan, A. C., 1996, Curr. Opin. Immunol., Vol. 8(3), pp. 394-401).
Three PTK receptors for VEGF have been identified: VEGFR-1 (Flt-1), VEGFR-2 (Flk-1 or KDR), and VEGFR-3 (Flt-4). These receptors are involved in angiogenesis and participate in signal transduction (Mustonen, T., et al., 1995, J. Cell Biol., Vol. 129, pp. 895-898).
Of particular interest is VEGFR-2, which is a transmembrane receptor PTK expressed primarily in endothelial cells. Activation of VEGFR-2 by VEGF is a critical step in the signal transduction pathway that initiates tumour angiogenesis. VEGF expression may be constitutive to tumour cells and can also be upregulated in response to certain stimuli.
One such stimuli is hypoxia, where VEGF expression is upregulated in both tumour and associated host tissues. The VEGF ligand activates VEGFR-2 by binding with its extracellular VEGF binding site. This leads to receptor dimerization of VEGFRs and autophosphorylation of tyrosine residues at the intracellular kinase domain of VEGFR-2. The kinase domain operates to transfer a phosphate from ATP to the tyrosine residues, thus providing binding sites for signalling proteins downstream of VEGFR-2 leading ultimately to initiation of angiogenesis (McMahon, G., 2000, The Oncologist, Vol. 5(90001), pp. 3-10).
Inhibition at the kinase domain binding site of VEGFR-2 would block phosphorylation of tyrosine residues and serve to disrupt initiation of angiogenesis.
TIE
Angiopoieten 1 (Ang1), a ligand for the endothelium-specific receptor tyrosine kinase TIE-2 is a novel angiogenic factor (Davis et al., 1996, Cell, Vol. 87, pp. 1161-1169; Partanen et al., 1992, Mol. Cell Biol., Vol. 12, pp. 1698-1707; U.S. Pat. Nos. 5,521,073; 5,879,672; 5,877,020; and 6,030,831). The acronym TIE represents “tyrosine kinase containing Ig and EGF homology domains”. TIE is used to identify a class of receptor tyrosine kinases, which are exclusively expressed in vascular endothelial cells and early hemopoietic cells. Typically, TIE receptor kinases are characterized by the presence of an EGF-like domain and an immunoglobulin (IG) like domain, which consists of extracellular folding units, stabilized by intra-chain disulfide bonds (Partanen et al., 1999, Curr. Topics Microbiol. Immunol., Vol. 237, pp. 159-172). Unlike VEGF, which functions during the early stages of vascular development, Ang1 and its receptor TIE-2 function in the later stages of vascular development, i.e., during vascular remodelling (remodelling refers to formation of a vascular lumen) and maturation (Yancopoulos et al., 1998, Cell, Vol. 93, pp. 661-664; Peters, K. G., 1998, Circ. Res., Vol. 83(3), pp. 342-343; Suri et al., 1996, Cell, Vol. 87, pp. 1171-1180).
Consequently, inhibition of TIE-2 would be expected to serve to disrupt remodelling and maturation of new vasculature initiated by angiogenesis thereby disrupting the angiogenic process.
Eph
The largest subfamily of receptor tyrosine kinases (RTKs), the Eph family, and their ligands (ephrins), play important roles in physiologic and pathologic vascular processes. Both the Ephs (receptors) and ephrins (ligands) are divided into two groups, A and B subfamilies (Eph Nomenclature Committee, 1997). The binding of ephrin ligands to Eph receptors is dependent on cell-cell interactions. The interactions of ephrins and Ephs have recently been shown to function via bi-directional signalling. The ephrins binding to Eph receptors initiate phosphorylation at specific tyrosine residues in the cytoplasmic domain of the Eph receptors. In response to Eph receptor binding, the ephrin ligand also undergoes tyrosine phosphorylation, so-called ‘reverse’ signalling (Holland, S. J., et al., 1996, Nature, Vol. 383, pp. 722-725; Bruckner et al., 1997, Science, Vol. 275, pp. 1640-1643).
Eph RTKs and their ephrin ligands play important roles in embryonic vascular development. Disruption of specific Eph receptors and ligands (including ephrin-B2) leads to defective vessel remodelling, organisation, and sprouting resulting in embryonic death (Wang, H. U., et al., 1998, Cell, Vol. 93, pp. 741-753; Adams, R. H., et al., 1999, Genes Dev, Vol. 13, pp. 295-306; Gale and Yancopoulos, 1999, Genes Dev, Vol. 13, pp. 1055-1066; Helbling, P. M., et al., 2000, Development, Vol. 127, pp. 269-278). Coordinated expression of the Eph/ephrin system determines the phenotype of embryonic vascular structures: ephrin-B2 is present on arterial endothelial cells (ECs), whereas EphB4 is present on venous ECs (Gale and Yancopoulos, 1999, Genes Dev, Vol. 13, pp. 1055-1066; Shin, D., et al., 2001, Dev Biol, Vol. 230, pp. 139-150). Recently, specific Ephs and ephrins have been implicated in tumour growth and angiogenesis.
The Ephs and ephrins have been found to be overexpressed in many human tumours. In particular, the role of EphB2 has been identified in small cell lung carcinoma (Tang, X. X., et al., 1999, Clin Cancer Res, Vol. 5, pp. 455-460), human neuroblastomas (Tang, X. X., et al., 1999, Clin Cancer Res, Vol. 5, pp. 1491-1496) and colorectal cancers (Liu, W., et al., 2004, Brit. J. Canc., Vol. 90, pp. 1620-1626), and higher expression levels of Ephs and ephrins, including EphB2, have been found to correlate with more aggressive and metastatic tumours (Nakamoto, M. and Bergemann, A. D., 2002, Microsc. Res Tech, Vol. 59, pp. 58-67).
Consequently, inhibition of EphB2 would be expected to serve to disrupt angiogenesis, and in particular in certain tumours where over-expression occurs.
The inventors have discovered compounds that, e.g., inhibit RAF (e.g., B-RAF) activity and/or are useful in the treatment of, e.g., proliferative disorders, cancer, etc.